1. L02: Tear break up time (BUT)
Mohammed A.M Aljarousha
Department of Optometry
Faculty of Allied Health Sciences
Islamic University-Gaza

2. Introduction Normal tear film is continuously available.
Blinking maintains the tear film continuity. However if you keep your eyes open long enough, without blinking, the tear film will start breaking up.
In patients with dry eyes the tear film is unstable, and breaks up faster. Therefore the tear break up time in patients who have dry eyes is short.

4. Method Make the patient sit in front of the slit lamp
Touch the lower bulbar conjunctiva with a fluorescein strip wetted with normal saline.
Ask the patient to blink several times and then stop.
set on a bright light setting with a cobalt blue filter.
count second until there a formation of dry spot , which appears black spot on the corneal surface.
tear film break up time is an indicator of the adequacy mucin component of tears

5. Interruption value more than 10 seconds is thought to be normal.
value of 5 to 10 seconds indicates border line.
value less than 5 seconds is dry line.

6. Blinking rate
Measured by counting the number of blinks during specific time.
Normal values 3 blinks every seconds.